question about lag

hI

i installed a mod named pixelmon in my pc its a very heavy mod as there are more then 1000 pokemons in it and i got 90 or more fps when i put on shaders i got 30 fps in 1.12.2 but when i switch to 1.16.4 and pla normal survival (vanilla) i get only 30fps without shaders

why do you think this happens?

umm a question, how can i have shaders without optifine?

so in the post i said that i get 30 fps with shaders in pixelmon means i already use optifine